Youcai Liu

High-sensitivity paracetamol sensor based on Pd/graphene oxide nanocomposite as an enhanced electrochemical sensing platform

Well-dispersed Pd nanoparticles were facilely anchored on graphene oxide (Pd/GO) via a one-pot chemical reduction of the Pd(2+) precursor without any surfactants and templates. The morphology and composition of the Pd/GO nanocomposite were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and energy dispersive analysis of X-ray (EDX). The stepwise fabrication process of the Pd/GO modified electrode and its electrochemical sensing performance towards paracetamol was evaluated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The experimental results indicate that the as-synthesized Pd nanoparticles are relatively uniform in size (5-10 nm) without large aggregation and uniformly distributed in the carbon matrix with the overall Pd content of 28.77 wt% in Pd/GO. Compared with the GO modified electrode, the Pd/GO modified electrode shows a better electrocatalytic activity to the oxidation of paracetamol with lower oxidation potential and larger peak current, so the Pd/GO nanocomposite can be used as an enhanced sensing platform for the electrochemical determination of paracetamol. The kinetic parameters of the paracetamol electro-oxidation at Pd/GO electrode were studied in detail, and the determination conditions were optimized. Under the optimal conditions, the oxidation peak current is linear to the paracetamol concentration in the ranges of 0.005-0.5 μM and 0.5-80.0 μM with a detection limit of 2.2 nM. Based on the high sensitivity and good selectivity of the Pd/GO modified electrode, the proposed method was successfully applied to the determination of paracetamol in commercial tablets and human urines, and the satisfactory results confirm the applicability of this sensor in practical analysis.

Facile synthesis of α-MoO3 nanobelts and their pseudocapacitive behavior in an aqueous Li2SO4 solution

α-MoO3 nanobelts were successfully prepared by a facile hydrothermal method with sodium molybdate (Na2MoO4) as the Mo source and NaCl as the capping agent. The as-prepared products were characterized using Fourier transformation infrared spectrophotometry (FT-IR), X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and selected area electronic diffraction (SAED) and their pseudocapacitive properties were investigated in a 0.5 M aqueous Li2SO4 solution by cyclic voltammetry (CV), chronopotentiometry (CP) and AC impendence. The results show that the dimensions of the as-prepared α-MoO3 nanobelts are 200–400 nm in width, ca. 60 nm in thickness and 3–8 µm in length. The redox potential for the α-MoO3 nanobelts is found in the range of −0.3 to −1.0 V vs. SCE, which indicates that the α-MoO3 nanobelts can be used as anode electrode materials for hybrid supercapacitors. The specific capacitances of the α-MoO3 nanobelts at 0.1, 0.25, 0.5 and 1 A g−1 are 369, 326, 256 and 207 F g−1, respectively. The maximum specific capacitance of the α-MoO3 nanobelts is much higher than those of MoO3 nanoplates with 280 F g−1, MoO3 nanowires with 110 F g−1 and MoO3 nanorods with 30 F g−1 recently reported in literature. Furthermore, the α-MoO3 nanobelt electrode exhibits a good cycle stability with more than 95% of the initial specific capacitance maintained after 500 cycles. Additionally, the present route to prepare nanostructured MoO3 is much less expensive than those with Mo powders as the Mo source. Overall, the obtained high performance α-MoO3 nanobelts could be a promising electrode material for supercapacitors.

Facile assembly of a 3D rGO/MWCNTs/Fe2O3 ternary composite as the anode material for high-performance lithium ion batteries

A three-dimensional (3D) reduced graphene oxide (rGO)/multi-walled carbon nanotubes (MWCNTs)/Fe2O3 ternary composite was fabricated by a facile, green and economical one-step urea-assisted hydrothermal approach as a promising anode material for high-performance lithium ion batteries. Designing and tailoring the 3D porous hierarchical nanostructure of rGO/MWCNTs/Fe2O3 contributes to a robust hybrid material with overwhelmingly superior electrochemical performances compared with bare Fe2O3, MWCNTs/Fe2O3, rGO/Fe2O3 and a physical mixture of rGO/Fe2O3 and MWCNTs, due to the strong synergistic effects among the individual component. The 3D rGO/MWCNTs/Fe2O3 composite exhibits highly enhanced specific capacity, cycling performance and rate capability: initial discharge and charge capacities of 1692 and 1322 mAh g−1 at 100 mA g−1, respectively, 1118 mAh g−1 after 50 cycles at 100 mA g−1 and 785 mAh g−1 at 1000 mA g−1. The assembling mechanism well illustrates the simple strategy, and the comprehensive electrochemical investigations further demonstrate its supernormal effectiveness, which could be extended to various transition metal oxides for energy storage and conversion.

One-step solution-phase synthesis of Co3O4/RGO/acetylene black as a high-performance catalyst for oxygen reduction reaction

On the way to become promising oxygen reduction reaction (ORR) catalysts, the hybrids composed of reduced graphene oxide (RGO) and transition metal oxides are suffering from stacking of RGO sheets. In this work, a Co3O4/RGO/acetylene black (AB) hybrid was successfully synthesized via a facile one-step solution-phase route with sandwiching of AB particles between the RGO sheets during the synthesis of Co3O4/RGO, which can effectively tackle the stacking of RGO sheets. Compared with Co3O4/RGO, Co3O4/RGO/AB-P (mixing AB with the pre-prepared Co3O4/RGO with stirring), Co3O4/RGO/AB-M (mixing AB with Co3O4/RGO during the fabrication of the Co3O4/RGO catalytic layer for ORR) and commercial 10 wt% Pt/C, the Co3O4/RGO/AB hybrid exhibits increases of 50.6%, 32.5%, 37.9% and 8.9% in the ORR current density, respectively. This indicates that the introduction strategy of AB to Co3O4/RGO plays a vital role in the enhancement of ORR catalytic activity. Moreover, the Co3O4/RGO/AB hybrid shows a subtle ascending trend in the ORR current density during continuous operation for 72 000 s, while Pt/C exhibits a 9.0% decrease. The exceptional ORR catalytic performance of Co3O4/RGO/AB can also be ascribed to the large specific surface area, well-anchored Co3O4 nanoparticles on the RGO sheets, and low ohmic and kinetic impedances for ORR. We hope this work will be conducive for the extensive commercial applications of fuel cells.